Process for the manufacture of high tenacity viscose rayon



Oct. 22,- 6 MAsA-roMo KUSUNOSE ETAL 3,107,970

PROCESS FOR THE MANUFACTURE OF HIGH TENACITY VISCOSE RAYON Filed Sept.28, 1961 United States Patent 3,107,970 PROCESS FOR THE MANUFACTURE OFHIGH TENACITY VISCOSE RAYON Masatomo Kusunose, Yasuo Saji, and TakeoKoyasu, all of Itano-gun, Tokushima, Japan, assign'ors to Toho RayonKabushiki Kaisha, Tokyo, Japan, a corporation of Japan Filed Sept. 28,1961, Ser. No. 141,356 Claims priority, application Japan Oct. 4, 1960 4Claims. (Cl. 1854) The present invention rel-ates to a process for themanufacture of viscose rayon, which comprises heating unaged viscose toa temperature above that of la spinning bath, extruding the thus heatedviscose in a low temperature acidic sulfate bath containingformaldehyde, and stretching the resulting threads in a second bath,namely in a double bath stretching method.

It is an object of this invention to provide regenerated viscose fiberscapable of supplying fabrics of high tenacity, high resistance to alkaliand excellent dimensional stability, in other words, to provide viscoserayon of high tensile strength, high dry and wet strength and goodresistance to alkali and high resistance to swelling.

Referring to the spinning of viscose to such a regenerated viscosefiber, particularly when :an excellent regenerated fiber is sought whichis appropriate for a certain specific purpose, it has usually beenWell-known to attain a close relationship between respective propertiesof the particular viscose and :a suitable coagulating and regeneratingmethod that is very well suitable for each property of the viscose,According to this invention, a type of viscose sufficiently removed ofso-called structure is shaped to filaments by an extremely slowregeneration and then by imparting resulting filaments crystallizationand arrangement eifects substantially simultaneously to impart theregenerated fiber a highly crystalline property and orienta tion.

In view of the above relationship, the substance of the presentinvention is based on a knowledge that an excellent fiber of a high wettensile strength can be obtained by heating a relatively insuificientlyaged viscose at high temperatures to decompose so-ca-lled structure forimproving dispersion property and regenerating by introducing thustreated viscose into a spinning bath which contains formaldehyde and iskept at a temperature lower than that of the viscose at least by 20 C.

Technical elements for this invention lie in close combination of theuse of viscose heated at high temperatures with the use of spinning bathcontaining formaldehyde and being held at a temperature lower than thatof the viscose at least by 20 C. The effect is remarkably highespecially in cases viscose of a relatively high polymerization degreeis treated, and regenerated fibers of excellent properties can beobtained.

The quantity of carbon bisulfide required for the manufacture of viscosein the practice of this invention ranges from 35 to 55% of the amount ofcellulose used and, in addition, no particularly high 'y-value isrequired.

The required alkali content of the viscose is in a range of 0.5 to 0.9times its content of cellulose, and a departure from such a rangeresults in degradation of the product obtained.

In particular, when low alkaline viscose is used which 3,107,970Patented Oct. 22., 1963 ice contains low alkali less than 0.5 times thecontent of cellulose, the dispersion of cellulose molecules in theviscose is unfavorable. Accordingly, a good result as referred to latercan not be obtained because the function of formaldehyde contained willthen be disturbed.

Moreover, unaged viscose of a salt index above 9 must be used.Furthermore, when the ripening is in progress, the quality of productslowers. With progress of ripening the structure develops un-favorably tothe practice of this invention similarly as described before.

High viscosity viscose, which viscosity varies from 50 to 400 secondsand preferably higher than 100 seconds, should be used. From viscose ofa viscosity below 50 seconds a fragile product of a poor knot strengthcan only 'be obtained. 1 According to the present invention, viscose isused after it has been heated from 45 to C. and a range from 55 to 66 C.is optimum. Various apparatus and methods are used for'hea-ting viscose.It is necessary to heat the viscose rapidly and uniformly as much aspossible near the spinneret.

Generally, viscose is heated by providing a heat exchanger whose heatsource is heated water in the neighborhood of the spinneret. Such heatedviscose should be spun in a spinning bath of a temperature held at least20 C. below that of the viscose. In this case, the thus heated viscoseis kept from being cooled by the low temperature of the spinning bath ata part of the viscose pipe immediately before the spinneret immersed inthe spinning bath.

The spinning bath according to this invention is 35 C. maximum bathcontaining from 50 to 150 gin/liter Na SO from 1. to 10 gm./ literformaldehyde, 30 gm./liter. max. ZnSO; and 40 gin/liter min. H

In thepresent process wherein formaldehyde is added to such a relativelylow temperature spinning ba-th, operational obstruction due to stimuloussmell of formaldehyde can be alleviated remarkably.

Attempts of raising polymerization degrees of cellulose moleculesconstituting regenerated fibers have long been made to improve thequality of products. In order to accomplish above'purpose, decrease ofthe cellulose concentr-ation in the viscose is avoided, which in turnrequires necessarily to spin high viscosity viscose.

Thus, a number of specific spinning processes for high viscosity viscosehave been introduced.

According to this invention, in which a viscose of such 'high viscosityas ranging from 50 to 400 seconds is spun under specific conditionsnecessary for this invention, no excellent property fiber anticipated bythis invention may be obtained by merely adding formaldehyde to thespinning bath. On the contrary, in many instances the quality of theproduct is lowered. The viscose is considered to require to receive theaction of a spinning bath which contains formaldehyde in the state of socalled decomposed structure as described before.

Principal functions of formaldehyde added to the spinning bath areconsidered to disturb the coagulation and formation of nuclei for 'OHradicals due to hydrogen bond or others of regenerated cellulose offilaments coming out from the spinning bath.

Since viscose is stretched in this unrestrained condition.

of OH-radicals in the second high temperature bath, it is consideredpossible to provide enough high tension and develop highly crystallinestructure and simultaneously attain a high degree of orientation.

Particularly when the viscosity of viscose increases, mutualconstraining of cellulose molecules in the viscose becomes high and theviscose includes much structure.

When such viscose as just referred to enters in a relatively lowtemperature spinning bath and is subject to reaction of formaldehyde,the constrainment received by the molecules in the viscose. isconsidered to act in such a way that the action of formaldehyde may bedisturbed. Therefore, in order to enable a relatively low temperaturespinning of a high viscosity viscose and obtain in addition an effectiveaction of formaldehyde, it is required to increase the temperature ofthe viscose at the spout of the spinning bath as compared with thetemperature of said bath.

When the temperature of the spinning bath is not within theabove-mentioned range, the spinning operation lacks smoothness to lowerthe quality of products. When the concentration of Na SO is less than 50gm./ liter, variation in concentration due to Na SO which occurs in thespinning bath is high and the process control and preparation of thespinning bath become difficult.

The essential requirement for the present invention is heating viscosein such a way that the temperature of the viscose entering the spinningbath may be at least 20 C. higher than that of the spinning bath andmoreover above 40 C. When the viscose is spun in an ordinary process, aremarkably inferior quality product can only be obtained as comparedwith the case with the present invention.

The present invention is carried out according to the double bathstretching spinning process and if necessary a third or a higher numberof baths may be used.

The most remarkable feature of the regenerated cellulose fiber obtainedin this invention is a high wet modulus. This is numerically compared bytension (grnz) per denier required for 5% elongation on theload-elongation curve (FIGURE 1) when wet.

TABLE 1 Load required for 5 extension when wet gm. denier- Product ofthe present invention Above 1.5 Ordinary viscose rayon 0.20 Usual highstrength staple fiber A 0.20 Usual high strength staple fiber B 0.70Usual high strength staple fiber C 0.90 Usual high strength staple fiberD 1.25

As the result of a further investigation on the process of thisinvention, the strength of the fiber manufactured by the process asdescribed above has been found to be dependent on the stretch conditionafter spinning.

Considering first over the stretching condition for spun filaments vs.strength of fibers obtained, the present inventor h z s made variousexperiments on the effect of the rates of stretching or elongations(percent) X, Y and Z upon the strength of the threads obtained. If thevelocity of filaments being reeled on the first spool from the firstbath is a m./'min.; that of the filaments being reeled on the secondspool after passing through the second 'bath (i.e. the first stretchingbath) is b m./min.; and that of the filaments being reeled on the thirdspool after passing through the third bath (i.e. the second stretchingbath) is c m./min., the elongation X (percent) in the first stretchingbathis:

the elongation Y (percent) in the second stretching bath is:

Y(percent) =(%1) X 100 and the total elongation Z (percent) is: z 1) x100 Therefore, a relational formula can be obtained:

X Y Z X Y m and H is used above 70 C. When each spun yarn is stretchedrespectively in the first and second stretching baths as strong aspossible within a limit where no local breakage of threads occur, Z willreach to the maximum.

It is evident that the excellent fiber can then be obtained. 7 7

Furthermore, in the relationship among elongations, X, Y and Z in eachbath, if X/Z exceeds 3/4, the breakage of threads will become noticeablein the second bath and no smooth spinning can not be expected, while if-X/Z is as low as below 1/ 4, the effect of elongation will not besufiicient as obvious in the following.

The relation between X and Z as just referred to has been ascertained tobe applicable when a plurality of stretching baths are used.

The results obtainable due to varying stretching conditions referred toabove for the spinning of yarn are shown in Table 2 in connection withembodiments of this inventio, as follows: These data compare each resultwith the spinning solution and spinning conditions being held the same.

TABLE2 a b c a f 4.55 4.35 1.15 4.68 3.21 3.18 2.86 :ass 1.34 1.16 1.581.48

5.8 as 1.9 6.2 so as 8.2 6.5 rss 1.7 1.13 1. 8

I The process of the present invention. a

b Hot weak acidic water baths are used at above C. for the second andthird baths; in the second bath, tion within which no local breakage ofthreads occurs is 180%. In thls case,stretching could not beefiected inthe third bath and the reeling was carried out around the final spool atthe velocity of 35 nth/mm. after passing same through the third bath.

0 Water bath was usedfor the second bath at 30 C and when the third bathused was the same as (a), the elongation was 80% in the second bath,while the third bath allowed a tolerance of 50% maximum elongation to beeflected.

Both the second and third baths were used at 90 0.; stretching was givenin the second bath and the maximum tolerance of 15% stretching was givenin the third bath. X/Z 1s 3.16, 4.

B The second bath was set as (a), while the temperature of the thirdFurthermore, according to the present invention, the

lowering of strength of fibers due to alkaline water solution is lessthan that of the original fiber. For instance, the above-mentionedfibers (a) and (b) were immersed in 5% aqueous NaOH solution at 20 C.for 10 minutes a without tension, thoroughly washed in dilute aceticacid and water and dried and then their strength was determined and theresult was shown as percentages to the corresponding strength of theoriginal sample as in'Ilable 3. The fibersaccording to this inventionshow evidently the maximum tolerance of elonga-- small lowering ofstrengths due to above mentioned alkali treatment.

TABLE 3 dry wet knot Specimens strength, strength, strength,

percent percent percent Example 1 Alkali which was prepared according tothe ordinary way by steeping, pressing, and shredding from wood pulp,was aged for a short interval of time, then xanthated and dissolved in50% by weight of cellulose of carbon bisulfide to produce viscosecomprising 7% cellulose and 4.5 alkali content. Such viscose was thenfiltered and defoamed, when the temperature was kept as low as possibleduring the Whole treatment from xanthation to spinning, and the viscoseof 218 second viscosity and 15 salt index was spun into a spinningsolution comprising 100 gm./liter Na SO 65 gm./liter H SO and 5gun/liter formaldehyde at 30 C. using a spinneret of 2000 holes of 0.065mm. diameter. Said viscose 'was passed directly before spinning througha heat exchanger having a heat source of hot water and a pipe groupsecured between a curved spinning pipe and candle filter and thetemperature of viscose was controlled to 60 C. at the outlet of thespinneret.

Such spun filaments were stretched to 230% in a slightly acidic secondbath at 90 C., reeled, cut and purified in an ordinary process. Thequalities of products thus obtained are shown under (e) of the followingtable.

When viscose was spun without heating in an entirely similar process, itwas impossible to stretch above 120% in the second bath; and as aresult, the resulting properties (6) were substantially the same asthose spun similarly as (c) but without addition of formaldehyde asshown in able (a). On the other hand, the qualities obtained byproceeding the ageing of viscose to a salt index of 7 show remarkabledegradation as shown in table (b).

As shown in (d) the properties of those spun in a similar process asthat of (e) but Without using formaldehyde were by far inferior to thoseobtained by the process under (e).

TABLE 4 Comparsion Process control control control control this processSalt index of viscose 15 7 15 15 15 Formaldehyde in spin-bath(gun/liter) 1. 0 5 5 0 5 Spinnerette, viscose temperature C 15 60 15 6060 1.25 1.25 1.25 1.25 1.25

dry 3. 37 2.38 3. 33 3. 73 5.02 wet 2. l4 1. 42 1. 98 2. 58 3. 60 0t 1.54 1.03 1.72 1.40 1. 74

y 8. 2 6. 8 7. 6 8. 1 6. 8 9.5 7. 8 7. 4 9. 8 6.1 Degree of swelling,percent 84 115 85 73 61 Load required for 5% wet elongation (gm/d.) 0.96 0.42 0.75 0.90 2. 85

Alkali cellulose, which was obtained by steeping and shedding from woodpulp in an ordinary process, was aged for a short interval of time andxanthated by using 38% carbon bisulfide of the weight of cellulose, thenviscose was prepared to 8% cellulose and 5% alkali.

Such viscose was filtered and deaerated, with the operationaltemperature being held as low as possible from dissolving to spinning.The viscose of 108 second viscosity, 14 salt index was spun into aspinning bath comprising 90 gm./liter N-a SO 75 =gm./liter H 80 15 V 6gm./liter ZnSO and 7 gm/liter formaldehyde at 32 C. through a spinnerethaving 4000 holes of 0.06 diameter.

Said viscose was heated at 63 C. at the spinneret directly beforespinning similarly as in Example 1.

The spun filaments were then passed through a slightlyfi acidic secondbath as 92 C. and stretched to 218% and reeled. Then, the resultingfilaments were cut and purified as usual. The results are shown in table(0). Table (a) shows the results obtained by spinnin in an entirelysimilar spinning bath excepting Na SO being 250 gm./ liter and H 95guru/liter.

Wood pulp was steeped, squeezed and shredded to ob- 'tain alkalicellulose. The resulting cellulose was aged in a short interval of timeand xanthated using 40% carbon bisulfide based on the weight ofcellulose used and further added 10% carbon bisulfide based on theweight of cellulose used at the beginning of xanthation. Such viscosecontained 7% cellulose and 4.5% alkali, which was filtered anddeaerated. The viscose was spun at viscosity 108 second and salt indexof 18.2.

The spinning was performed at the operational temperature held as low aspossible in a treatment from xanthation to spinning and in the spinningbath containing 65 gm./liter H SO '95 gin/liter N-a SO and 6 gm./ literformaldehyde at 28 0., through a 4000 hole spinneret of 0.06 diameter.

Said viscose was heated immediately before spinning to 56 C. by passingthrough a heat exchanger secured between a gear pump and curved spinningpipe, of which heat source was hot water.

Spun filaments were passed through a second 2-meter bath containing 30gin/liter H S0 and 50 gn1./liter Na SO at 30 C., While stretching wasgiven to the filaments. Further, said filaments Were passed through athird bath of 1.5 meters, containing 60 gm./ liter H 80 and 100gm./liter Na SO at 90 C., while the filaments were imparted 50%stretching.

In this case, the total stretching in the second and third baths are 245The filaments were reeled around the final spool at a velocity of 35art/min. and cut and purified by usual process. In this case, theproperties of the filaments were as shown in Table 2.

What we claim is:

1. A process for manufacturing high tenacity viscose rayon filamentscomprising heating to a temperature in the range of between 45 C. and 70C. an unripened viscose having a salt index above 9 and having aviscosity ranging from 50 to 400 seconds, said viscose having an alkalicontent ranging from 0.5 to 0.9 times the cellulose content, thenspinning said viscose in its heated state into an acid coagulating bathheld at a temperature in the range of between a maximum of 35 C. and aminimum of below the viscose temperature by at least 20 C., said acidcoagulating bath containing from 50 to gm./liter Na SO from 1 to 10gm./liter formaldehyde, 30 gm./liter maximum. ZnSO, and 40 gm./literminimum H 80 3,107,970 7 8 2. The process as recited in claim 1, whereinsp-un 4. The process -as recited in claim 1 wherein the temfilamentsfrom said amid coagulating bath are stretched peratusre to which saidunripened viscose is heated is in in a second bath at a temperaturebelow 50 C. conthe range of between 552C. and 60 C.

g gg 3 36 gm-liner H2804 and from 30 References Cited in the file ofthis patent gm. 1 er a2 4.

3. The process as recited in claim 2, wherein spun 5 UNITED STATESPATENTS filaments from said second bath are stretched in a third2,611,928 M ion t a1. Sept, 30, 1952 bath at a temnerature above 70 C.containing the sa ne 2,705,184 Drisch et a1 Mar. 29, 1955' ccfmttgnts assgid second baht:1 gvlgcrlelm the strbetchmg 2,937,070 Cox May 17, 1960o i e spun aments 1n sai 1r 2 a ranges etween one-fourth andthreefourths of the total stretching in 10 FOREIGN PATENTS both thesecond and third baths. 854,152 Great Britain Nov. 16, 1960

1. A PROCESS FOR MANUFACTURING HIGH TENACITY VISCOSE RAYON FILAMENTSCOMPRISING HEATING TO A TEMPERATURE IN THE RANGE OF BETWEEN 45*C. AND70*C. AN UNRIPENED VISCOSE HAVING A SALT INDEX ABOUT 9 AND HAVING AVISCOSITY RANGING FROM 50 TO 400 SECONDS, SAID VISCOSE HAVING AN ALKALICONTENT RANGING FROM 0.5 TO 0.9 TIMES THE CELLULOSE CONTENT, THENSPINNING SAID VISCOSE IN ITS HEATED STATE INTO A ACID COAGULATING BATHHELD AT A TEMPERATURE IN THE RANGE OF BETWEEN A MAXIMUM OF 35*C. AND AMINIMUM OF BELOW THE VISCOSE TEMPERATURE BY AT LEAST 20*C., SAID ACIDCOAGULATING BATH CONTAINING FROM 50 TO 150 GM./LITER NA2SO4, FROM 1 TO10 GM./LITER FORMALDEHYDE, 30 GM./LITER MAXIMUM ZNSO4 AND 40 GM./LITERMINIMUM H2SO4.